I just ordered the "wrong" memory for a Macbook I am upgrading. The original config is 1 GB RAM (2x512 MB) and I wanted to upgrade to 4GB RAM (2x2GB). I ordered a single 4GM RAM stick by mistake though and while my first thought was to exchange it, I am now wondering if it is preferred to keep the 4GB stick and combine it with one of the old ones. Wondering about differences in performances and general pros and cons. Note though that I will not upgrade this laptop anymore and the RAM is 200 pin so it will not be moved over to the next laptop as it will likely use 204 pin RAM. I did read the "understanding RAM guide" but it does not give a consistent answer.